Transition scheme for position sensorless control of AC motor drives

Abstract

Motor drive control apparatus and methods are presented for sensorless control of a driven motor using open loop current regulated control during low-speed operation and an EMF-based position observer for position estimation during higher speed operation, with zero feedback speed during low-speed open-loop operation and feedback speed estimated by the EMF-based observer during high-speed operation and with velocity mode control over the full speed range and mode control hysteresis for smooth transitions between open loop and EMF-based observer control.

The following is claimed: 
     
       1. A method for sensorless motor speed control in a motor drive having an inverter, the method comprising:
 generating a first position signal or value from a desired frequency or motor speed signal or value; 
 generating a second position signal or value using an EMF-based position estimator according to inverter output current signals or values and inverter output voltage signals or values; 
 generating voltage command signals or values for pulse width modulation operation of the inverter using a speed controller according to a desired speed signal or value, a feedback speed signal or value, and a selected commutation position signal or value; 
 setting the selected commutation position signal or value to the first position signal or value in a first mode for a first range of speeds or to the second position signal or value in a second mode for a second higher range of speeds according to the desired speed signal or value; 
 setting the feedback speed signal or value to a fixed value for open loop control in the first mode for the first range of speeds; and 
 computing the feedback speed signal or value according to the second position signal or value for closed loop control in the second mode for the second range of speeds. 
 
     
     
       2. The method of  claim 1 , comprising presetting an integrator of a position generator according to the second position signal or value for transitioning from the second mode to the first mode. 
     
     
       3. The method of  claim 2 , wherein the fixed value is zero. 
     
     
       4. The method of  claim 1 , wherein the fixed value is zero. 
     
     
       5. A method for sensorless motor speed control in a motor drive having an inverter, the method comprising:
 generating a first position signal or value from a desired frequency or motor speed signal or value; 
 generating a second position signal or value using an EMF-based position estimator according to inverter output current signals or values and inverter output voltage signals or values; 
 generating voltage command signals or values for pulse width modulation operation of the inverter using a speed controller according to a desired speed signal or value, a feedback speed signal or value, and a selected commutation position signal or value; 
 setting the selected commutation position signal or value to the first position signal or value in a first mode for a first range of speeds or to the second position signal or value in a second mode for a second higher range of speeds according to the desired speed signal or value; 
 setting the feedback speed signal or value to a fixed value for open loop control in the first mode for the first range of speeds; and 
 computing the feedback speed signal or value according to the second position signal or value for closed loop control in the second mode for the second range of speeds; 
 wherein the first range and the second range overlap, the method comprising switching from the first mode to the second mode when an absolute value of the desired speed signal or value exceeds a first threshold, and switching from the second mode to the first mode when the absolute value of the desired speed signal or value is less than a second threshold, the second threshold being lower than the first threshold. 
 
     
     
       6. The method of  claim 5 , comprising blending the first and second position signals or values to compute the selected commutation position signal or value for transitioning from the first mode to the second mode. 
     
     
       7. The method of  claim 6 , wherein the first and second position signals or values are blended to provide a smooth transition of the selected commutation position signal or value. 
     
     
       8. The method of  claim 6 , comprising presetting an integrator of a first position generator according to the second position signal or value for transitioning from the second mode to the first mode. 
     
     
       9. The method of  claim 8 , wherein the fixed value is zero. 
     
     
       10. The method of  claim 6 , wherein the fixed value is zero. 
     
     
       11. The method of  claim 5 , comprising presetting an integrator of a position generator according to the second position signal or value for transitioning from the second mode to the first mode. 
     
     
       12. The method of  claim 11 , wherein the fixed value is zero. 
     
     
       13. The method of  claim 5 , wherein the fixed value is zero. 
     
     
       14. A method for sensorless motor speed control in a motor drive having an inverter, the method comprising:
 generating a first position signal or value from a desired frequency or motor speed signal or value; 
 generating a second position signal or value using an EMF-based position estimator according to inverter output current signals or values and inverter output voltage signals or values; 
 generating voltage command signals or values for pulse width modulation operation of the inverter using a speed controller according to a desired speed signal or value, a feedback speed signal or value, and a selected commutation position signal or value; 
 setting the selected commutation position signal or value to the first position signal or value in a first mode for a first range of speeds or to the second position signal or value in a second mode for a second higher range of speeds according to the desired speed signal or value; 
 setting the feedback speed signal or value to a fixed value for open loop control in the first mode for the first range of speeds; 
 computing the feedback speed signal or value according to the second position signal or value for closed loop control in the second mode for the second range of speeds; and 
 blending the first and second position signals or values to compute the selected commutation position signal or value for transitioning from the first mode to the second mode. 
 
     
     
       15. The method of  claim 14 , wherein the first and second position signals or values are blended to provide a smooth transition of the selected commutation position signal or value. 
     
     
       16. The method of  claim 15 , comprising presetting an integrator of a position generator according to the second position signal or value for transitioning from the second mode to the first mode. 
     
     
       17. The method of  claim 16 , wherein the fixed value is zero. 
     
     
       18. A motor drive controller, comprising:
 at least one processor operatively coupled with an electronic memory; 
 a position calculation component implemented using the at least one processor and operative to generate a first position signal or value using a position generator implemented using the at least one processor according to a desired frequency or motor speed signal or value, the position generator being operative to generate a second position signal or value using an EMF-based position estimator implemented using the at least one processor according to inverter output current signals or values and inverter output voltage signals or values; and 
 a command generator component implemented using the at least one processor and operative to generate voltage command signals or values for pulse width modulation operation of an inverter using a speed controller according to a desired speed signal or value, a feedback speed signal or value, and a selected commutation position signal or value; 
 wherein the position calculation component is operative to set the selected commutation position signal or value to the first position signal or value in a first mode for a first range of speeds or to the second position signal or value in a second mode for a second higher range of speeds according to the desired speed signal or value; 
 wherein the command generator component is operative to set the feedback speed signal or value to a fixed value for open loop control in the first mode for the first range of speeds; and 
 wherein the command generator component is operative to compute the feedback speed signal or value according to the second position signal or value for closed loop control in the second mode for the second range of speeds. 
 
     
     
       19. The controller of  claim 18 , wherein the first range and the second range overlap, and wherein the command generator component is operative to switch from the first mode to the second mode when an absolute value of the desired speed signal or value exceeds a first threshold, and to switch from the second mode to the first mode when the absolute value of the desired speed signal or value is less than a second threshold, the second threshold being lower than the first threshold. 
     
     
       20. The controller of  claim 18 , wherein the position calculation component is operative to blend the first and second position signals or values to compute the selected commutation position signal or value for transitioning from the first mode to the second mode.